1. Field of the Invention
The present invention relates to an exposure apparatus and device manufacturing method.
2. Description of the Related Art
In recent years, as the capacity of a semiconductor memory increases as well as the speed and integration density of a CPU processor, a demand for a decrease in feature size of a resist pattern formed on a wafer increases, which requires a high exposure accuracy. Also, a high throughput is needed inevitably. Therefore, improvements in exposure accuracy and throughput have been achieved by increasing the resolution through an increase in numerical aperture (NA) of projection optical systems, an improvement in position controllability, or an increase in acceleration speed of a substrate stage or original state, and the like.
When driving the stage of the exposure apparatus, an inertia reaction force occurs upon acceleration/deceleration. When the reaction force is transmitted from the floor or an exposure apparatus main body to a surface plate on which a projection optical system and measurement system are placed, the surface plate may swing or vibrate. This excites natural vibration of the mechanism of the exposure apparatus which may then become high-frequency vibration that interferes with high-speed, high-accuracy positioning of the stage.
In order to solve problems related to the reaction force, a conventional exposure apparatus is provided with a structure that receives the reaction force. The reaction force generated upon driving of the stage is released to this structure. As a result, the vibration of the floor caused by the reaction force upon driving of the stage is reduced. Japanese Patent Laid-Open No. 11-297587 discloses this technique.
The above prior art can decrease the vibration of the floor, on which the exposure apparatus is installed, caused by the reaction force generated upon driving of the stage. If, however, a base frame which supports an anti-vibration mount has a natural frequency equal to that of the installation floor, it may amplify the floor vibration. Then, the entire exposure apparatus may be excited to interfere with high-speed, high-accuracy positioning of the stage. In other words, to decrease the influence of the vibration by a disturbance such as floor vibration, the base frame which supports the anti-vibration mount must have a natural frequency which is equal to or more than the natural frequency (e.g., 20 Hz to 40 Hz) of the floor.
When paying attention to the shape of the base frame (the supporting member of an anti-vibration mechanism) of a conventional example, a supporting member 3′ of an anti-vibration mount is connected as shown in FIG. 4. Therefore, a vibration mode occurs in the connecting portion. The natural vibration of the connecting portion amplifies the vibration of the floor, thus interfering with high-speed, high-accuracy positioning of the stage.
In recent years, a stage apparatus is available which has two stages to increase the processing speed and throughput of an exposure apparatus. This enables an exposure process of projecting a pattern onto a substrate and exposing the projected pattern and an alignment process of aligning the substrate to be performed simultaneously.
As described above, as the stage size increases, the size of the main body structure must be increased to cope with it. The size of the main body structure, however, cannot be increased limitlessly because the occupied installation area may undesirably increase and because of the limitations on the withstand load of the building. When the stage size increases, the rigidity of the main body structure tends to decrease.